System and method for adjusting clearance in a gas turbine

ABSTRACT

A system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets is disclosed. The system includes: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an elongated member extending from the turbine shell. The at least one shroud segment is attached to an end of the elongated member, the elongated member configured to move in response to a temperature change to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to gas turbines and, moreparticularly, to methods and systems for adjusting clearance betweenbucket or blade tips and a shroud assembly connected to a turbine shell.

In order to improve efficiency, gas turbines, such as those used inpower generation or aviation, utilize a turbine “shroud” disposed in aturbine shell. The shroud provides for a reduced clearance between thetips of buckets disposed on the turbine rotor and the shroud incomparison to a clearance between the bucket tips and the turbine shell.Such reduced clearance provides enhanced efficiency by maintaining areduced threshold clearance between the shroud and tips of the bucketsto prevent unwanted “leakage” of hot gas over tips of the buckets.Increased clearances can lead to gas leakage which can reduce turbineefficiency.

Current shroud systems employ solely segmented shrouds connected to theturbine shell and held together by, for example, turbine shell hooks.The clearance between the bucket tips and the shroud is simply driven bythe thermal time constant behavior between the turbine shell androtor/buckets. Initial bucket tip/shroud clearances may be set highenough to prevent rubbing, but such clearances cannot be activelycontrolled in transient or in steady state conditions. Both turbineshell out-of-roundness and transient bucket/shroud rubbing play a majorrole in increased steady state clearances. Cold-built clearances, i.e.,clearances set prior to operation, can be set high enough to mitigaterubbing, but, in effect, this will drive up steady state clearances, andthereby reduce engine efficiency and output. Accordingly, there is aneed for improved systems and methods for controlling clearance betweenbucket tips and shrouds in a gas turbine, such as during transientand/or steady state operation of the turbine.

BRIEF DESCRIPTION OF THE INVENTION

A system for adjusting a clearance in a gas turbine including a turbinerotor and a plurality of buckets, constructed in accordance withexemplary embodiments of the invention includes: a shroud assemblyincluding at least one shroud segment, the at least one shroud segmentbeing disposed in an interior of a turbine shell; and an elongatedmember extending from the turbine shell. The at least one shroud segmentis attached to an end of the elongated member, the elongated memberconfigured to move in response to a temperature change to move theshroud segment and change a clearance between the shroud segment and atleast one of the plurality of buckets.

Other exemplary embodiments of the invention include a method ofadjusting a clearance in a gas turbine including a turbine rotor and aplurality of buckets. The method includes: disposing a shroud assemblyon a turbine shell, the shroud assembly including a shroud segmentattached to one end of an elongated member; extending the elongatedmember from the turbine shell and disposing the shroud segment in aninterior of a turbine shell; and applying a thermal source to the shroudassembly to move the shroud segment and change a clearance between theshroud segment and at least one of the plurality of buckets.

Additional features and advantages are realized through the techniquesof exemplary embodiments of the invention. Other embodiments and aspectsof the invention are described in detail herein and are considered apart of the claimed invention. For a better understanding of theinvention with advantages and features thereof, refer to the descriptionand to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gas turbine in accordance with anexemplary embodiment of the invention;

FIG. 2 is a side view of an exemplary embodiment of a shroud assemblycoupled to the gas turbine of FIG. 1;

FIG. 3 is a side view of another exemplary embodiment of the shroudassembly of FIG. 2;

FIG. 4 is an axial and side view of another exemplary embodiment of theshroud assembly of FIG. 2;

FIG. 5 is an axial and side view of another exemplary embodiment of theshroud assembly of FIG. 2, including exemplary values for clearancebetween a shroud and a turbine shell;

FIG. 6 is a side view of a further exemplary embodiment of the shroudassembly of FIG. 2;

FIG. 7 is a side view of another exemplary embodiment of the shroudassembly of FIG. 2;

FIG. 8 is a side view of another exemplary embodiment of the shroudassembly of FIG. 2;

FIG. 9 is a side view of another exemplary embodiment of the shroudassembly of FIG. 2;

FIG. 10 is an axial view of an exemplary embodiment of a coolingconfiguration of the shroud assembly of FIG. 2;

FIG. 11 is an axial view of another exemplary embodiment of the coolingconfiguration of FIG. 10;

FIG. 12 is an axial view of another exemplary embodiment of the coolingconfiguration of FIG. 10;

FIG. 13 is an illustration of a system for controlling clearance betweena shroud and a bucket tip in a gas turbine; and

FIG. 14 is a flow chart providing an exemplary method for controllingclearance between a shroud and a bucket tip in a gas turbine.

DETAILED DESCRIPTION OF THE INVENTION

There is provided a system and method for displacing a component in aturbine or other system. The system includes a thermally actuated memberthat is configured to move in response to a temperature change. In oneembodiment, a coefficient of thermal expansion (“CTE”) of the thermallyactuated member is different than the CTE of one or more structuresattached thereto. A method is provided that includes heating or coolingthe thermally actuated member to cause movement of the member. In oneembodiment, the thermally actuated member is an elongated member such asa rod or cylinder.

In one embodiment, the system includes the thermally actuated memberconnected at one end to a turbine shell or other body, and connected atanother end to a movable member such as a turbine shroud, to adjust aclearance between bucket tips and one or more shrouds located on a gasturbine. Although bucket tips are described herein, the system may beutilized with any type of bucket, blade or other device for causingmovement of a turbine rotor. The elongated member is described herein asa generally cylindrical rod or tube, but may be any suitable shapehaving a dimension in the radial direction. As used herein, the term“radial” refers to a direction extending from the center of the turbinerotor or a rotational axis of the turbine rotor, and perpendicular tothe major axis or the rotational axis of the turbine rotor. Although thethermally actuated member is described herein in conjunction withturbine assemblies, the thermally actuated member may be utilized inconjunction with any system or apparatus utilizing displacement ofcomponents.

With reference to FIG. 1, a gas turbine assembly constructed inaccordance with an exemplary embodiment of the invention is indicatedgenerally at 10. The gas turbine assembly 10 includes a turbine shell 12which is held in place around a compressor 14 and a power turbine 16,which are connected by a rotor 18. A combustion chamber 20 is formedbetween the compressor 14 and turbine 16 sections of the assembly 10. Aplurality of rotor blades or buckets 39 are connected to the turbine 16via, for example, a rotor disk. The turbine shell 12 includes aplurality of shroud assemblies 30 attached to an interior portion of theturbine shell 12 and defining a clearance “C” between the shroudassembly 30 and the buckets 39.

Referring to FIG. 2, a shroud assembly 30 is disposed in the turbineshell 12. The shroud assembly 30 includes one or more shroud segments31, each of which is removably attached to an elongated member 32 by anysuitable mechanism, such as a bayonet attachment or a threadedattachment. The elongated member 32 extends radially from the turbineshell 12 toward the bucket 39. The shroud segment 31 is separated fromthe bucket 39, and the distance between a tip of the bucket 39 definesthe clearance “C” between the inner shroud 40 and the bucket tip. Theelongated member 32 has a coefficient of thermal expansion (“CTE”) thatis different from the CTE of the turbine shell 12 and/or othercomponents. In one embodiment, the elongated member 32 has a CTE that isgreater than the turbine shell 12. The elongated member 32 is expandableand/or retractable by selecting a temperature of the elongated member tocontrol the clearance C between the shroud segment 31 and the bucket 39.

Referring to FIG. 3, in one embodiment, the elongated member 32 extendsradially from an exterior wall 42 and through a tube 44 formed throughthe turbine shell 12 and a protrusion 46 such as a boss. The radiallength of the protrusion 46 is selected, in one embodiment, to increasethe radial length of the elongated member 32 and thereby increase oradjust the amount of displacement of the elongated member 32 in responseto changes of temperature. In this embodiment, the protrusion 46 is madefrom a material, such as an alloy, having a higher CTE than that of theelongated member 32. In one embodiment, an electric heater 48 isdisposed in contact with the protrusion 46, so that heat can be appliedto the elongated member 32 and/or the protrusion 46 to control theexpansion of the elongated member 32 and/or the protrusion 46.

In one embodiment, the elongated member 32 has a coefficient of thermalexpansion (“CTE”) that is different from the CTE of the protrusion 46and or the turbine shell 12. For example, as shown in FIG. 4, theelongated member 32 has a CTE that is less than the CTE of theprotrusion 46. By selecting the CTE of each component, the amount ofextension of the inner shroud 40 is controllable relative to the amountof heating or cooling applied. For example, because the elongated member32 has a CTE that is less than the CTE of the protrusion 46, heat can beapplied to the protrusion 46 to control displacement of the shroudassembly 30 without the elongated member 32 providing any significantcontribution to the displacement. In one embodiment, the elongatedmember 32 has a CTE that is sufficiently low so that displacement issubstantially a result of heating the protrusion 46.

Referring to FIG. 4, another embodiment of the shroud assembly 30 isdisposed in the turbine shell 12. In this embodiment, the one or moreshroud segments 31 each include the elongated member 32, an outer shroud34 attached to the interior wall 36 of the turbine shell 12, anintermediate shroud 38 attached to the elongated member 32, and an innershroud 40 attached to the intermediate shroud 38. In one embodiment, theintermediate shroud 38 is removably attached to the elongated member byany suitable mechanism, such as a bayonet attachment or a threadedattachment. The inner shroud 40 is separated from a bucket 39, and thedistance between a tip of the bucket 39 defines the clearance betweenthe inner shroud 40 and the bucket tip.

In one embodiment, the shroud assembly 30 includes any number ofsegments 3 1, and each segment 31 includes at least one elongated member32 and at least one of the shrouds, 34, 38, 40. In the example shown inFIG. 2, the shroud assembly 30 forms a ring shroud having fourquadrants. Each segment 31 includes one elongated member 32, one outershroud 34, one intermediate shroud 38, and six inner shrouds 40. Thenumber and size of segments 31, and the number of elongated members 32and shrouds 34, 3 8, 40 described in the embodiments herein is exemplaryand is not limited.

In one embodiment, an inlet 50 is included to allow heated air or steamfrom the interior of the turbine shell 12 or allow other heating orcooling sources. Such sources may include air, gas and steam.

In one embodiment, a securing or adjusting mechanism 52 is attached tothe elongated member 32. The mechanism 52 is connectable to theprotrusion 46 to allow the elongated member 32 to be manually ormechanically moved or removed from the shroud assembly 30.

In another embodiment, insulation 54 is provided to thermally isolatethe elongated member 32 from the protrusion 46, and heating or coolingsources can be applied to the elongated member 32 via the inlet 50.Alternatively, this embodiment allows for air from the interior of theturbine shell 12 to maintain the elongated member 32 at a specifiedtemperature, and retract the elongated member 32 by applying heat to theprotrusion 46 and causing the protrusion 46 to expand and therebyretract the elongated member 32. For example, during transientoperation, the electric heater 48 is turned on at the time of maximumpinch between the bucket tip and the inner shroud 40 to expand theprotrusion 46 and cause the elongated member 32 to retract. In thisembodiment, the elongated member 32 has a CTE that is less than the CTEof the protrusion 46.

Referring to FIG. 5, another embodiment of the shroud assembly 30 isshown. In this embodiment, the elongated member 32 is a hollowcylindrical rod disposed in the tube 44. The tube 44 extends through theturbine shell 12, and is sealed from the exterior of the turbine shellby a cap 56. In one embodiment, the tube 44 extends partially throughthe interior of the wall of the turbine shell, and is thus sealed by thewall itself. The elongated member 32 is attached to the intermediateshroud 38 and is secured in position by a positioning mechanism 58. Theelongated member 32 may be connected to the positioning mechanism 58 bya mechanical attachment, such as a threaded or bayonet attachment, ormay simply act as a centering mechanism and protrude into the tube 44 toprevent the elongated member from moving about an axis of the tube 44.Heating or cooling sources can be applied to the inlet 50 to adjust thetemperature of the elongated member 32.

In one example, the elongated member 32 has a radial height of nineinches, the turbine shell has a radial height of six inches, and theouter shroud has a radial height of three inches.

Referring to FIG. 6, another embodiment of the shroud assembly 30includes the elongated member 32 that extends through the protrusion 46and the turbine shell 12, and is attached to the intermediate shroud 38.The elongated member 32 is attached to the securing or adjustingmechanism 52. As shown in this embodiment, the intermediate shroud 38forms a “u” shape that may be designed to define a distance by which theelongated member can be retracted. In addition to adjusting temperatureand providing selected materials having selected CTEs, this featureprovides another mechanism by which to control movement of the innershroud 40. In one embodiment, the shroud assembly includes a purgingsystem 60. The purging system includes a purge conduit to allow coolingair or other material to be applied to the intermediate and innershrouds 38, 40.

Referring to FIG. 7, another embodiment of the shroud assembly 30includes an elongated member conduit 64 extending through a portion ofthe length of the elongated member 32. This partially hollow elongatedmember 32 includes a solid portion at an end of the elongated member 32located at or near an exterior of the turbine shell 12. In thisembodiment, gas from the turbine shell interior and/or other thermalsources may be applied through the inlet 50 to the interior of theelongated member 32, with the exterior end of the elongated member 32preventing the thermal source from escaping to the exterior of theturbine shell 12.

In another embodiment of the shroud assembly 30, the outer shroud 34 ispocketed and includes a pin 66 or other fastening mechanism thatattaches the outer shroud 34 to the turbine shell 12. The pin 66 isremovable in an axial direction, to in turn allow the outer shroud 34 tobe removed axially so that components such as the inner shroud 40 can beaccessed. Additional pins or other fastening mechanisms are included toattach the intermediate shroud 38 to the elongated member 32.

Referring to FIG. 8, yet another embodiment of the shroud assembly 30includes a hollow elongated member 32 having a conduit 64 extendingalong the entire length of the elongated member 32. In this embodiment,discharge gas from the turbine 10, cooling air, gas or steam, or othermaterials can be applied to the interior of the elongated member 32 froman exterior of the turbine shell 12. In one embodiment, stabilizingprotrusions 68, such as one or more individual protrusions or a ring,protruding toward the interior of the elongated member conduit areincluded to assist in stabilizing the elongated member 32 within thetube 44.

In another embodiment, the securing or adjusting mechanism includes alocking feature 70 attached to an alignment feature 71, which allows theelongated member to be mechanically or manually aligned within the tube44 and/or allows the elongated member 32 to be advanced or retractedradially to adjust the clearance between the inner shroud 40 and thebucket tips. In another embodiment, the elongated member 32 is a solidelongated member.

Referring to FIG. 9, another embodiment of the shroud assembly 30includes the locking/alignment cap 70, another embodiment of thestabilizing protrusions 68 which are separately constructed and attachedto the turbine shell 12, and pins 66. An additional pin 72 is providedto secure the intermediate shroud 38 to the elongated member 32 andallow for axial removal of the pin 72 for removal of the intermediateshroud 38. In one embodiment, shroud conduits 74 are provided to allowgas from the interior of the turbine shell 12 or from other sources toenter the tube 44 and exit through the intermediate shroud 38.

FIGS. 10-12 provide configurations of the shroud assembly 30 includingcooling applications for cooling the inner shrouds 40. In each of theseconfigurations, the shroud assembly includes a plurality of intermediateshrouds 38 and a plurality of inner shrouds 40 forming a ring.

FIG. 10 illustrates a configuration including hollow elongated members32 through which a cooling source 78 such as air, gas or steam can beintroduced to the inner shrouds 40. In this embodiment, a single hollowelongated member 32 is associated with each intermediate shroud 38. Theshroud assembly 30, for example, includes twenty intermediate shrouds 38and one hundred inner shrouds 40.

Referring to FIG. 11, another embodiment of the shroud assembly 30includes two hollow elongated members 32 per intermediate shroud 38, andalso includes a cavity 80 in the intermediate shroud 38 through whichthe cooling source 78 can be introduced to the inner shrouds 40. In thisembodiment, the cooling source 78 can enter and exit through the hollowelongated members 32, and can also enter through the cavity 80. Theshroud assembly 30, for example, includes ten intermediate shrouds 38and one hundred inner shrouds 40.

In one embodiment, if there are two or more elongated members 32 pershroud assembly 30, the elongated members 32 extend parallel to oneanother. The average of the angular deviation of each elongated member32 from a radial line extending from the rotational axis is equal tozero. This orientation helps to prevent possible binding duringoperation. For example, if a third elongated member 32 is placed halfway between the first two elongated members 32, the third elongatedmember 32 is oriented along the radial line, and all of the elongatedmembers 32 are parallel to one another.

FIG. 12 shows another embodiment of the cooling scheme, including asingle elongated member 32 per intermediate shroud 38, and a singlecavity 80 per intermediate shroud 38. In another embodiment, any numberof elongated members and/or cavities 80 are included with eachintermediate shroud 38.

Referring to FIG. 13, there is provided a system 90 for controlling aclearance between a shroud 34, 38, 40 and one or more bucket tips. Thesystem may be incorporated in a computer 91 or other processing unitcapable of receiving data from users or from sensors incorporated withthe shroud assembly. A displacement sensor 92 is also coupled to thecomputer 91 so that the computer 91 can control the shroud assembly 30to achieve or maintain a desired clearance. In one embodiment, theshroud assembly includes or is operably connected to a heating mechanismsuch as the electric heater 48 and/or a relay or other switch connectedto an electrical power source. The computer 91, in one embodiment, alsois connected to and able to control sources of thermal energy, such asthe electric heater 48 and gas, steam and/or air sources. The processingunit may be included with the shroud assembly 30 or included as part ofa remote processing unit.

In one embodiment, the system 90 includes a computer 91 coupled to adevice such as the displacement senor 92 to measure the clearancebetween the bucket tip and the shroud assembly 30. Exemplary componentsinclude, without limitation, at least one processor, storage, memory,input devices, output devices and the like. As these components areknown to those skilled in the art, these are not depicted in any detailherein.

In one embodiment, the computer 91 is configured to automaticallyretract the inner shroud 40 to an initial position upon detection of amalfunction in the shroud assembly 30.

Generally, some of the teachings herein are reduced to instructions thatare stored on machine-readable media. The instructions are implementedby the computer 91 and provide operators with desired output.

FIG. 14 illustrates an exemplary method 100 for adjusting a clearance ina gas turbine including a turbine rotor and a plurality of buckets. Themethod 100 includes one or more stages 101-104. In an exemplaryembodiment, the method includes the execution of all of stages 101-104in the order described. However, certain stages may be omitted, stagesmay be added, or the order of the stages changed. In the exemplaryembodiments described herein, the method is described in conjunctionwith the shroud assembly 30 and the computer 91. However, the method 100may be performed in conjunction with any type of processor or performedmanually.

In the first stage 101, the shroud assembly 30 is disposed on theturbine shell 12. The elongated member 32 is extended through at least aportion of the wall of the turbine shell 12 and the inner shroud ispositioned in the interior of the turbine shell 12.

In the second stage 102, the elongated member 32 is initially disposedto a selected radial distance from the interior of the turbine shell 12.In one embodiment, this is accomplished by disposing the shroud assembly30 and designating the radial distance of the outer shroud 34, theintermediate shroud 38 and/or the inner shroud 40 so that a selectedminimum distance is set. In one embodiment, this may be accomplished bymoving the elongated member 32 radially through the tube 44. In oneembodiment, the minimum distance is selected based on the maximum pinchbetween the bucket tip and the inner shroud 40, that is, the closestapproach between the bucket tip and the inner shroud 40.

In the third stage 103, the turbine 10 is activated. Activation in turncauses rotation of the turbine rotor and the buckets 39.

In the fourth stage 104, a thermal source such as the electric heater46, steam, air and gas is applied to the shroud assembly 30 to move theinner shroud 40 and change a clearance between the inner shroud 40 andat least one of the plurality of buckets tips. In one embodiment, athermal source is applied to the elongated member 32 to raise thetemperature of the elongated member, causing it to expand and advancethe inner shroud 40 toward the interior of the turbine shell 12 toreduce the clearance between the inner shroud 40 and the bucket tips. Inanother embodiment, the thermal source is applied to the elongatedmember 32 to reduce its temperature to retract the inner shroud 40 awayfrom the interior of the turbine shell 12.

In one embodiment, the electric heater 46 is activated to elevate thetemperature of the protrusion 46 and/or the elongated member 32. Inresponse, the elongated member expands and extends in the radialdirection to decrease the clearance between the inner shroud and thebucket tip. In one embodiment, a thermal source is applied to theelongated member via the protrusion 46 and/or the inlet 50, to extend orretract the inner shroud 40. As discussed above, applying a heatingsource will raise the temperature of the elongated member and extend theinner shroud 40, and applying a cooling source will lower thetemperature of the elongated member and retract the shroud 40.

In one embodiment, the elongated member is maintained at a selectedtemperature, such as by applying air from the interior of the turbineshell 12 through the conduit 50, and the elongated member 32 isretracted by applying heat to the protrusion 46 and causing theprotrusion 46 to expand and thereby retract the elongated member 32. Forexample, during transient operation, the electric heater 48 is turned onat the time of maximum pinch between the bucket tip and the inner shroud40 to expand the protrusion 46 and cause the elongated member 32 toretract.

Although the systems and methods described herein are provided inconjunction with gas turbines, any other suitable type of turbine may beused. For example, the systems and methods described herein may be usedwith a steam turbine or turbine including both gas and steam generation.

The system and method described herein provide numerous advantages overprior art systems. For example, the systems and methods provide thetechnical effect of allowing active control of the clearance between thebucket tip and the shroud, which will allow a user to run the turbineengine at tighter clearances than prior art systems. These systems andmethod are a simple and inexpensive means of moving the shroudsindependently to control clearances and to account for manufacturingdifferences.

The systems and methods described herein allow for tighter clearancesthan prior art systems, which increases overall efficiency relative toprior art designs. Prior art systems employ solely segmented shroudsheld together by turbine shell hooks. The clearance is simple driven bythe thermal time constant behavior between the turbine shell androtor/buckets. Bucket tip/shroud clearances may be set high enough toprevent rubbing, but clearances may not be actively controlled intransient, nor in steady state conditions. The systems and methodsdescribed herein are advantageous in that they provide for activecontrol of the shroud assembly during both transient and steady stateconditions.

The capabilities of the embodiments disclosed herein can be implementedin software, firmware, hardware or some combination thereof As oneexample, one or more aspects of the embodiments disclosed can beincluded in an article of manufacture (e.g., one or more computerprogram products) having, for instance, computer usable media. The mediahas embodied therein, for instance, computer readable program code meansfor providing and facilitating the capabilities of the presentinvention. The article of manufacture can be included as a part of acomputer system or sold separately. Additionally, at least one programstorage device readable by a machine, tangibly embodying at least oneprogram of instructions executable by the machine to perform thecapabilities of the disclosed embodiments can be provided.

In general, this written description uses examples to disclose theinvention, including the best mode, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of exemplaryembodiments of the invention if they have structural elements that donot differ from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

1. A system for adjusting a clearance in a gas turbine including aturbine rotor and a plurality of buckets, the system comprising: ashroud assembly including at least one shroud segment, the at least oneshroud segment being disposed in an interior of a turbine shell; and anelongated member extending from the turbine shell; wherein the at leastone shroud segment is attached to an end of the elongated member, theelongated member configured to move in response to a temperature changeto move the shroud segment and change a clearance between the shroudsegment and at least one of the plurality of buckets.
 2. The system ofclaim 1, wherein a coefficient of thermal expansion (CTE) of theelongated member is different than the CTE of the turbine shell.
 3. Thesystem of claim 1, wherein the elongated member extends through theturbine shell in a radial direction, the radial direction being normalto a major axis of the turbine rotor.
 4. The system of claim 1, furthercomprising a tube extending through at least a portion of the turbineshell, the elongated member extending through the tube.
 5. The system ofclaim 4, wherein a coefficient of thermal expansion (CTE) of theelongated member is different than the CTE of the tube.
 6. The system ofclaim 1, wherein the elongated member is selected from a hollow rod anda solid rod.
 7. The system of claim 1, further comprising a protrusionattached to an exterior of the turbine shell and attached to theelongated member, and an electric heat source in thermal communicationwith the protrusion for changing the temperature of at least one of theprotrusion and the elongated member.
 8. The system of claim 1, whereinthe at least one segment includes an outer shroud attached to theturbine shell, an intermediate shroud attached to the elongated member,and an inner shroud attached to the intermediate shroud.
 9. The systemof claim 1, further comprising an inlet through at least one of theelongated member and the turbine shell for introducing a thermal sourceto the elongated member.
 10. The system of claim 9, wherein the thermalsource is selected from at least one of steam, air and gas.
 11. Thesystem of claim 1, wherein the shroud assembly includes a plurality ofshroud segments configured to form a ring.
 12. The system of claim 1,further comprising an adjustment device at a connection point betweenthe elongated member and the turbine shell, the adjustment deviceconfigured to be engaged to move the elongated member relative to theturbine shell.
 13. The system of claim 1, further comprising at leastone additional elongated member extending from the turbine shell andattached to the at least one shroud segment, wherein both the elongatedmember and the at least one additional elongated member extend in anaverage direction parallel to a radial direction extending from arotational axis of the gas turbine.
 14. A method of adjusting aclearance in a gas turbine including a turbine rotor and a plurality ofbuckets, the method comprising: disposing a shroud assembly on a turbineshell, the shroud assembly including a shroud segment attached to oneend of an elongated member; extending the elongated member from theturbine shell and disposing the shroud segment in an interior of aturbine shell; and applying a thermal source to the shroud assembly tomove the shroud segment and change a clearance between the shroudsegment and at least one of the plurality of buckets.
 15. The method ofclaim 14, wherein applying the thermal source includes applying thethermal source to the elongated member to elevate a temperature of theelongated member to cause the shroud segment to move radially toward aninterior of the turbine shell.
 16. The method of claim 14, whereinapplying the thermal source includes applying the thermal source to theelongated member to reduce a temperature of the elongated member tocause the shroud segment to move radially away from an interior of theturbine shell.
 17. The method of claim 14, wherein the shroud assemblyincludes a protrusion attached to an exterior of the turbine shell andattached to the elongated member.
 18. The method of claim 17, whereinapplying the thermal source includes applying the thermal source to theprotrusion to cause the protrusion to thermally expand and move theelongated member radially away from the interior of the turbine shell.19. The method of claim 14, wherein disposing the shroud segmentincludes determining a maximum pinch between the bucket tip and theshroud segment, and disposing the shroud segment at an initial radiallocation based on the maximum pinch.
 20. The method of claim 19, furthercomprising retracting the shroud segment to the initial position upon amalfunction of the shroud assembly.